How Barrier Islands Work

Satellite view of the barrier islands that form North Carolina's Outer Banks. Seemore pictures of beaches.

Photo courtesy NASA

Barrier islands, sometimes called barrier spits, are found on coastlines all over the world, but are most noticeable along the eastern coast of North America, where they extend from New England down the Atlantic Coast, around the Gulf of Mexico and south to Mexico.

Barrier islands are popular vacation spots, including resort communities from Atlantic City, New Jersey, to Miami Beach, Florida. Many people own vacation homes or condominiums on barrier islands, and more barrier islands are being developed for tourism. However, barrier islands are fragile, constantly changing ecosystems that are important for coastal geology and ecology. Development has posed dangers to these ecosystems and has also increased the risk of property damage every year from hurricanes and Nor'easters.

In this article, we will examine the fragile ecosystems of barrier islands. We'll explore how these islands are formed, what habitats and life are present on them, how they change, the consequences of development and the recreational activities that attract tourists to them every year.

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Barrier island beach

Photos courtesy USGS

Barrier islands are long, narrow, offshore deposits of sand or sediments that parallel the coast line. Some barrier islands can extend for 100 miles (160 km) or more. The islands are separated from the main land by a shallow sound, bay or lagoon. Barrier islands are often found in chains along the coast line and are separated from each other by narrow tidal inlets, such as the Outer Banks of North Carolina.

The formation of barrier islands is complex and not completely understood. The current theory is that barrier islands were formed about 18,000 years ago when the last Ice Age ended. As the glaciers melted and receded, the sea levels began to rise, and flooded areas behind the beach ridges at that time. The rising waters carried sediments from those beach ridges and deposited them along shallow areas just off the new coast lines. Waves and currents continued to bring in sediments that built up, forming the barrier islands. In addition, rivers washed sediments from the mainland that settled behind the islands and helped build them up.

Barrier islands serve two main functions. First, they protect the coastlines from severe storm damage. Second, they harbor several habitats that are refuges for wildlife.